diff --git a/regression/orig/test055.log b/regression/orig/test055.log
new file mode 100644
index 000000000..12decc137
--- /dev/null
+++ b/regression/orig/test055.log
@@ -0,0 +1,2 @@
+0
+3
diff --git a/regression/test055.expr b/regression/test055.expr
new file mode 100644
index 000000000..00b21a292
--- /dev/null
+++ b/regression/test055.expr
@@ -0,0 +1,8 @@
+fun len(l) {
+  case l of
+     _ : xs -> return len(xs) + 1
+    |{} -> return 0 
+  esac
+}
+write(len({}));
+write(len({1, 2, 3}))
\ No newline at end of file
diff --git a/regression/test055.input b/regression/test055.input
new file mode 100644
index 000000000..e69de29bb
diff --git a/runtime/runtime.c b/runtime/runtime.c
index f339db8b7..a9e51ad70 100644
--- a/runtime/runtime.c
+++ b/runtime/runtime.c
@@ -66,7 +66,7 @@ char* de_hash (int n) {
   static char *chars = (char*) BOX (NULL);
   static char buf[6] = {0,0,0,0,0,0};
   char *p = (char *) BOX (NULL);
-  chars =  "_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNJPQRSTUVWXYZ";
+  chars =  "_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
   p = &buf[5];
 
 #ifdef DEBUG_PRINT
@@ -316,13 +316,16 @@ extern void* Bsexp (int n, ...) {
 
 extern int Btag (void *d, int t, int n) {
   data *r = (data *) BOX (NULL);
-  r = TO_DATA(d);
+  if (UNBOXED(d)) return BOX(0);
+  else {
+    r = TO_DATA(d);
 #ifndef DEBUG_PRINT
-  return BOX(TAG(r->tag) == SEXP_TAG && TO_SEXP(d)->tag == t && LEN(r->tag) == n);
+    return BOX(TAG(r->tag) == SEXP_TAG && TO_SEXP(d)->tag == t && LEN(r->tag) == n);
 #else
-  return BOX(TAG(r->tag) == SEXP_TAG &&
+    return BOX(TAG(r->tag) == SEXP_TAG &&
 	     GET_SEXP_TAG(TO_SEXP(d)->tag) == t && LEN(r->tag) == n);
 #endif
+  }
 }
 
 extern int Barray_patt (void *d, int n) {
diff --git a/src/X86.ml b/src/X86.ml
index 0d02f765b..87c9d9873 100644
--- a/src/X86.ml
+++ b/src/X86.ml
@@ -389,7 +389,7 @@ module M = Map.Make (String)
 
 (* Environment implementation *)
 class env =
-  let chars          = "_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNJPQRSTUVWXYZ" in
+  let chars          = "_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ" in
   let make_assoc l i = List.combine l (List.init (List.length l) (fun x -> x + i)) in
   let rec assoc  x   = function [] -> raise Not_found | l :: ls -> try List.assoc x l with Not_found -> assoc x ls in
   object (self)